The identification of cell surface antigens shared by components of the lymphoid, musculo-skeletal, and/or central nervous systems offers the possibility of (1) exploring multisystem membrane abnormalities through the investigation of lymphoid cells, easily obtained and purified; (2) defining subpopulations through the preparation of fluoresceinated reagents and subsequent analysis on the fluorescence activated cell sorter (FACS); and (3) clarifying the role of sub-populations in disease states affecting both the lymphoid and central nervous systems. These investigative areas are being pursued in projects exploring immunologic abnormalities in dystrophic mice, the distribution of Gm1 ganglioside on lymphocytes, and the effects of neurotropic influenza A on the immune system.